The use of focused ion-beam (FIB) microscopes has become common for the preparation of specimens for later analysis in the transmission electron microscope (TEM). The structural artifacts, and even some structural layers, in the device region and interconnect stack of current integrated-circuit devices can be too small to be reliably detected with the secondary electron imaging in a Scanning Electron Microscope (SEM), or FIB, which offers a bulk surface imaging resolution of approximately 3 nm. In comparison, TEM inspection offers much finer image resolution (<0.1 nm), but requires electron-transparent (<300 nm thick) sections of the sample mounted on 3 mm diameter grid disks.
The in-situ lift-out technique is a series of FIB milling and sample-translation steps used to produce a site-specific specimen for later observation in a TEM or other analytical instrument. During in-situ lift-out, a wedge-shaped section (the “lift-out sample”) of material containing the region of interest is first completely excised from the bulk sample, such as a semiconductor wafer or die, using ion-beam milling in the FIB. This lift-out sample is typically 10×5×5 μm in size. Removal of the lift-out sample is then typically performed using an internal nano-manipulator in conjunction with the ion-beam assisted chemical-vapor deposition (CVD) process available with the FIB tool.
The process of in-situ lift-out is a procedure of several successive steps, where the starting point is the delivery of a wafer, having the area of interest, and the probe tip inside the FIB vacuum chamber, and the end point is the lift-out sample ready for the TEM investigation. There is a need in the industry to have the entire process automated, thus allowing for fast and safe processing of a lift-out sample without the need to vent the vacuum chamber or to remove the probe and sample through an airlock.
The reader should note, however that the field of application is limited neither to automated lift-out systems, nor to semiconductor samples. Other objects of interest could be micro-mechanical systems, or biological specimens. Further, in-situ lift-out can be carried out in an atmosphere instead of a vacuum, when the nature of the specimen permits.